In order to accurately determine network usage statistics, network administrators use methods such as host discovery. Host discovery can be performed manually or in an automated fashion. Automated methods are often used when large address spaces are present. A method of host discovery on an Internet Protocol (IP) network might include sending a short message to every potential host address on a network, and then waiting for a response. Such a message generally takes the form of an Internet Control Message Protocol (ICMP) ping.
Typical Ethernet network devices have an associated Media Access Control (MAC) address, which functions as a serial number for the network interface of the network device. MAC addresses are assigned to network interfaces at the time of manufacture or in some cases, can be programmed into the network interface at a later time. Devices on a network are each assigned an IP address, so that they can be uniquely identified in the same address space as other devices on the network. IP address assignment is typically performed by a Dynamic Host Configuration Protocol (DHCP) server. Internet Protocol Version 4 (IPv4) is the protocol currently used in most networks and allows for a maximum of 232 (4.3×109) usable addresses. A method of expanding the address space is to use a private subnet, which allows private addresses to be distributed on a local area network (LAN) and publicly associated with a single IP address on a public network.
Internet Protocol Version 6 (IPv6) supports 2128 (3.4×1038) addresses. Because of the length of the IPv6 address, device specific identifiers such as a MAC address may be included in the IPv6 address. Additionally, network specific identifiers such as a local-prefix may be included in the IPv6 address. Because of the significantly larger address space, many more addresses may be used on a network. Currently, many systems that employ IPv6 addresses continue to use IPv4 addresses. This is known as a dual stack environment, wherein both IPv4 addresses and IPv6 addresses are assigned to devices.